A low-temperature solution process technique is employed to develop an inorganic cesium carbonate (Cs2CO3) as an electron transport material for inorganic-organic hybrid double cation (FAPbI(3))(0.85)(MAPbBr(3))(0.15) perovskite solar cells, as an alternative to the conventional thick and meso-TiO2. A device structure of compact-TiO2/Cs2CO3 (0.2 wt. %)/perovskite/spiro-OMETAD leads to enhanced performance of the photovoltaic device, achieving a short-circuit current density (J(sc)) of 22.26 mA/cm(2), an open-circuit voltage (V-oc) of 1054 mV, a fill factor (FF) of 71.6%, and a power conversion efficiency (PCE) of about 17% under one sun illumination, whereas the controlled device structure shows an efficiency of 16.58% without such surface modification layer. Additionally, a device structure of Cs2CO3 (6 wt. %)/perovskite/spiro-OMETAD without any TiO2 ETM has shown a J(sc) of 15.40 mA/cm(2), V-oc of 1023 mV, FF of 51.7%, and a PCE of 8.14%. On the other hand, external quantum efficiency (EQE) data yields around 85% of incident photon to electron conversion for c-TiO2/Cs2CO3 (0.2 wt. %)/perovskite/spiro-OMETAD structure and integrated J(sc) extracted from EQE data confirms that J(sc) obtained from the current-voltage test is within a close agreement. The obtained results indicate that there is a possibility to further increase the performance of perovskite-based cells and reduce their processing cost by replacing the thick mesoporous TiO2 by Cs2CO3. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)